Summary The float-equipped Cessna 180H (registration N720CS, serial number 18052165) took off from Cordingley Lake, Ontario, at 0905 eastern daylight time on a local flight with the pilot and two passengers on board. The owner of the aircraft, a licensed pilot, occupied the right rear seat, and a second passenger, also a licensed pilot, was in the right front seat. After completing the engine run-up checks, the take-off run was commenced without backtracking. After liftoff, the aircraft reached tree-top height but would not continue to climb or accelerate. As the aircraft crossed the shoreline and made initial contact with the tops of trees, full flaps were selected and the aircraft nose was raised so that the floats would absorb the impact. The floats struck the trees and the aircraft pitched nose-down and struck the ground in a near-vertical attitude. The three occupants received minor injuries. A small, post-impact, fuel-fed fire occurred forward of the firewall; the fire did not spread beyond that localized area. Ce rapport est galement disponible en franais. Other Factual Information History of Flight The weather, as locally reported, was as follows: wind from the south at 10 to 12knots, the sky mostly clear, and the temperature approximately 20C. The lake surface, which was somewhat sheltered by the surrounding trees, was reported to be calm. The aircraft's floats were pumped out as part of the pre-flight checks. The aircraft was taxied to the north end of the lake and turned into wind for run-up checks of magneto and propeller operations. The aircraft travelled approximately 1000feet during these checks. At 0905 eastern daylight time1 , it began its take-off run with approximately 4000feet remaining to the shoreline (see AppendixA - Aircraft Take-off Path). Flap setting was 20. The aircraft came up on the step normally. The right float was rolled off the water; then it settled back. The right float was rolled off again and the aircraft became airborne at a speed of approximately 60 mph. The actual water run was approximately 2000feet. After the aircraft was airborne, it accelerated to about 65 mph and climbed to about tree-top height. It then stopped accelerating or climbing and the airspeed decreased to about 60 mph. The aircraft was turned 20 to 30 to the left to take advantage of lower terrain in that direction. The distance remaining to the shoreline was considered to be too short to permit a safe landing straight ahead. As the aircraft crossed the shoreline and made initial contact with the tops of trees, full flap (40) was lowered and the controls were pulled aft in an attempt to slow the aircraft and cushion the impact by striking with the bottom of the floats first. The engine remained at full power. Accident Aircraft N720CS, a Cessna 180H, was equipped with Canadian Aircraft Products (CAP) series 3000D floats. It was powered by a Teledyne Continental O-470-R normally-aspirated, reciprocating engine and was fitted with a 78-inch, three-blade Hartzell propeller. The CAP series 3000D floats were approved under supplemental type certificate (STC) SA1749WE. The three-blade propeller was approved under STC SA00852AT. The aircraft was also equipped with bubble door windows (STC SA00897CH) and a short take-off and landing kit (STC SA967CE). During the investigation, these two STCs were assessed as having negligible effect on the performance of the aircraft. All STCs associated with N720CS contained a standard limitation and condition as follows: The approval of this change in the type design applies basically to the aircraft models listed on the relevant FAA approved master eligibility list and should not be extended to other specific models of these airplanes on which other previously approved modifications are incorporated, unless it is determined that the interrelationship will introduce no adverse effect upon the airworthiness of that aircraft. For the accident flight, the aircraft's take-off weight was calculated to be 2935 pounds and the centre of gravity was calculated to be at 42.1inches aft of the datum. Records indicate that it was serviced and maintained in accordance with existing directives. There were no reports of aircraft discrepancies prior to or during the flight. There were no discrepancies with the flight control system or indications that the engine was performing abnormally. The owner reported satisfactory performance of the aircraft when the three-blade propeller was installed and it was in a land-plane configuration. However, when the floats were installed, there was a loss of performance that was subjectively characterized as being equivalent to carrying an extra 300-pound load. The accident aircraft was equipped with lap belts and shoulder harnesses for the two front seats, and lap belts for the two rear seats. The pilot and front-seat passenger wore the lap belts and shoulder harnesses. Each received a minor injury to the knee adjacent to the pedestal, but neither had face or head injuries. The owner, in the rear seat, had the lap belt fastened and received minor facial injuries. They were able to walk to the shoreline where they were rescued by a person who had observed the crash. Aircraft Certification The Cessna 180H aircraft was issued with type certificate number 5A6 by the United States Civil Aeronautics Board under the authority of Civil Air Regulation, part 3. The FAA has the authority to issue STCs under the provisions of Federal Aviation Regulation, part 21. Any person who alters a product by introducing a major change in type design not great enough to require a new application for a type certificate under section 21.19 shall apply to the Administrator for a supplemental type certificate, except that the holder of a type certificate for the product may apply for amendment of the original type certificate. The type certificate data sheet (TCDS) for the Cessna 180H indicates that the Continental O-470-R is one of two different engine models approved for the 180H. The TCDS also lists ten different two-blade propellers of diameters varying from 82inches to 88inches, six of which have no limitations associated and four of which are applicable only to the O-470-R engine. Two additional propellers are listed for aircraft that have been reworked in accordance with specific Cessna Service Kits that were not applicable to the accident aircraft. The TCDS lists one landplane version, two floatplane versions, and one amphibious float version of the model 180H. There was no requirement in the certification criteria for an approved aircraft flight manual (AFM). Cessna provided an owner's manual (OM) for the model 180H which depicts only the landplane equipped with wheels. This OM does not cover float or ski configurations, but states that OM supplements are provided to cover operation of other optional equipment. The OM has an operational data section with performance charts for the landplane, but the performance figures do not indicate that they are for a particular engine or propeller. There is a table on the inside front cover of the OM entitled Performance-Specifications. This table lists the engine as a Continental O-470-R and the propeller as an 82-inch diameter constant-speed. There is nothing elsewhere in the OM that addresses engine-propeller combinations. Specifically, the operating limitations section has no restrictions that prohibit any engine-propeller combination. In the TCDS, there are no restrictions as to which propeller can be installed on any of the versions of the aircraft. Cessna provided an OM supplement2 for the model 180 equipped as a floatplane, amphibian, or skiplane. This supplement is applicable to the floats that are listed in the TCDS, one of which is the Edo model 249A-2870. The operational data section of this supplement has performance charts for the model 180 floatplane. The only propeller installed by Cessna for the factory-delivered float installation is the 88-inch, two-blade propeller. The only mention of engine or propeller is inside the front cover of the OM supplement in the Performance-Specifications table where it lists the engine as a Continental O-470-R and the propeller as 88-inch diameter constant-speed. There is nothing elsewhere in the floatplane OM supplement that addresses engine-propeller combinations. The operating limitations section has no restrictions that prohibit any engine-propeller combination. According to the Cessna OM supplement performance charts, for the gross weight, lake elevation, and atmospheric conditions at the time of the accident, the water run distance required for take-off was 1050feet, and the total distance required to clear a 50-foot obstacle was 1800feet. STC Integration and Performance Implications CAP Series 3000D STC The CAP series 3000D floats were installed under an STC and therefore are not mentioned in the Cessna OM supplement for floatplanes. The approved AFM supplement for the CAP series 3000D float states that performance equals or exceeds that with the Edo model 249A-2870 floats, which are similar to the model 249A-2870 floats that are listed in the Cessna floatplane OM supplement. As originally written and approved in 1968, the CAP series 3000D STC specified a maximum gross weight of 2820 pounds for the Cessna model 180H seaplane, the same maximum gross weight as stated in the Cessna OM supplement for the floatplane on Edo model 249A-2870 floats. The CAP series 3000D STC was later amended to provide a gross weight limit of 2950 pounds and an approved centre of gravity range of 38.8inches to 43.9inches aft of the datum. The CAP series 3000D STC stated that the performance of the aircraft with CAP series 3000D floats was equal to or better than that with Edo model 249A-2870 floats. The Cessna 180OM supplement for the floatplane provides performance charts up to a gross weight of 2950 pounds, but contains a note that the maximum gross weight for the Edo model 249A-2870 floats is 2820 pounds. The investigation was unable to determine what performance tests or engineering analyses were carried out to substantiate the gross weight increase for the CAP series 3000D floats. Three-Blade Propeller STC The three-blade propeller was installed under an STC issued to the former Bonaire Aviation Company. The STC is now owned by Hartzell Propeller Inc. The STC has no limitation as to applicability to floatplane configurations. The associated installation instructions referred to both land and sea configurations for changing markings on the tachometer. The associated AFM supplement states that original aircraft placards apply to information that is not addressed in the supplement. In operating limitations, the AFM supplement presents the same tachometer markings as the installation instructions, but refers to land and amphibian configurations rather than land and sea. In the operational data section, the AFM supplement states that "performance. . .equals or exceeds the performance with the original engine or propeller." Supporting documentation for the approval of the STC indicates that this statement was based on a comparison of the efficiency of the three-blade, 78-inch propeller with various two-blade, 82-inch propellers that were approved for the Cessna 180; it did not compare the three-blade, 78-inch propeller with two-blade, 88-inch propellers. Hartzell Propeller Inc. analytically compared the three-blade, 78-inch propeller and a two-blade, 88-inch propeller and predicted a loss of about 3% thrust at take off conditions. Analysis by the FAA estimated the following performance effects: Climb rate during initial climb reduced by 50feet per minute; Take-off water run increased by 50feet; Air distance from lift-off to a height of 50feet increased by approximately 150feet; and Total take-off distance to clear a 50-foot obstacle increased by approximately 200feet or about 10%. The three-blade, 78-inch propeller would not provide performance equivalent to the two-blade, 88-inch propeller that was the basis for the floatplane version. Therefore, a floatplane equipped with the three-blade, 78-inch propeller could not achieve the performance specifications depicted in the Cessna floatplane supplement. According to the three-blade propeller STC, engineering analysis, supported by tests at representative speeds, had demonstrated that the three-blade propeller provided performance equal to or better than approved performance charts in the Cessna180 OM3. The OM performance charts cover a wide range of engine and propeller combinations that are approved by the FAA for installation in the Cessna 180. As part of this investigation, propeller manufacturers were contacted and they indicated that some combinations, including longer-diameter, two-blade propellers, likely provide noticeably better performance than shown on the charts. Take-Off Procedure According to the Cessna floatplane supplement, the recommended take-off procedure is to use 20 flap, accelerate and lift-off at 50 to 60 mph, climb at 65 mph to clear obstacles, and retract the flaps slowly after reaching a safe altitude and airspeed. If lift-off is difficult due to high lake elevation or glassy water, the supplement recommends rolling one float out of the water first. Through experience with the three-blade propeller on floats, the owner's usual take-off technique on N720CS was to roll one float off at 55 mph, raise the flaps to 10 as soon as airborne, and keep the nose down to accelerate to 80 mph before beginning to climb. Pilot Experience The pilot held a private pilot's licence valid for single-engine land and seaplanes. He had approximately 500 hours of flying time, most of which were on a float-equipped Cessna 185 that he owned. He had three hours on the Cessna 180, including a check flight flown the previous day with the owner of N720CS. The check flight was completed in another Cessna 180 that also belonged to the owner of N720CS. The aircraft used for the check flight differed in that it had an 88-inch McCauley two-blade propeller, Edo model 2960 floats, standard windows, and no short take-off and landing kit. For the check flight on the previous day, the take-off weight of the aircraft was lighter, as there were only two persons on board. The fuel load was similar and there was less cargo. The take-off was performed with 20 of flap in accordance with the AFM float supplement. The aircraft flew off without needing to be rolled onto one float, accelerated to 80 mph, and climbed. Flaps were retracted while climbing through 200feet. This take-off procedure is similar to that used by the pilot in his own Cessna 185, except that he uses only 10 of flap in the Cessna 185 during the water run. The pilot was not informed about the need (on the accident aircraft) to retract the flaps to 10 in order to accelerate and climb.